Conventionally, for example in Japanese Unexamined Patent Application Publication No. 2010-260378A, a pneumatic tire is disclosed in which a plurality of protrusions (projections) extending in the tire radial direction is provided at predetermined intervals in the tire circumferential direction on the tire side portion (tire side surface) on the inner side in the vehicle width direction when the tire is mounted on a vehicle, and a plurality of recesses is provided over the tire circumferential direction and the tire radial direction on the tire side portion on the outer side in the vehicle width direction when the tire is mounted on a vehicle. When mounted on a vehicle, air flows uniformly toward the rear on the outer side in the vehicle width direction, but on the inner side in the vehicle width direction, the tire is disposed within the tire house, and other components such as the axle and the like are disposed nearby, so the flow of the air is easily disturbed. According to this pneumatic tire, an air distribution promotion effect and rectification effect are obtained and the air resistance is reduced by the protrusions provided on the tire side portion on the inner side in the vehicle width direction where the air flow is easily disturbed, and turbulent flow is produced when the vehicle is traveling by the recesses provided on the tire side portion on the outer side in the vehicle width direction, the drag force that tends to pull the tire backward due to the low pressure portion produced to the rear of the tire when traveling is reduced, so the fuel consumption is improved.
Also, conventionally, for example in Japanese Unexamined Patent Application Publication No. 2009-029380A, a pneumatic tire is disclosed in which ridges are formed to generate turbulent flow in the tire side portion. These ridges for generating turbulence in Japanese Unexamined Patent Application Publication No. 2009-029380A include a plurality of inner side ridges disposed at intervals along the tire circumferential direction in a region on the inner side in the tire radial direction from the maximum tire width position, and a plurality of outer side ridges disposed at intervals along the tire circumferential direction in a region on the outer side in the tire radial direction from the maximum tire width position. Also, the plurality of inner side ridges is disposed so that the extension direction of each of the inner side ridges coincides with the tire radial direction, and the plurality of outer side ridges is disposed so that the extension direction of each of the outer side ridges is inclined with respect to the tire radial direction, and outer side ridges adjacent to each other are disposed with the opposite orientation of the inclination with respect to the tire radial direction. As a result of the inner side ridges, turbulent flow is generated on the region on the inner side in the tire radial direction from the maximum tire width position of the pneumatic tire, and the cooling is good. In addition, as a result of the outer side ridges, in the region to the outer side in the tire radial direction from the tire maximum width position of the pneumatic tire, reattachment of the air flowing in the tire circumferential direction to the tire side portion surface is facilitated, and the flow speed of the air flowing from the inner side to the outer side in the tire radial direction is increased, so the cooling is good.
By providing protrusions on the tire side portion as in the pneumatic tire disclosed in Japanese Unexamined Patent Application Publication No. 2010-260378A as described above, it is possible to improve the fuel economy, but the protrusions are disposed extending in the tire radial direction, so in the ground contact portion that contacts the road surface, the stiffness in the tire radial direction is locally increased in the tire circumferential direction and the uniformity is reduced, and there is a possibility that vibrations could be easily generated when traveling. Also, in the pneumatic tire disclosed in Japanese Unexamined Patent Application Publication No. 2009-029380A the inner side ridges are disposed so that the extension direction of the inner side ridges coincides with the tire radial direction, so likewise the uniformity is reduced, and there is a possibility that vibrations could be easily generated when traveling which could reduce the riding comfort. Moreover, in the pneumatic tire disclosed in Japanese Unexamined Patent Application Publication No. 2009-029380A, ridges are not provided at the maximum tire width position. According to the research of the inventors and others, it was found that the maximum tire width position is the portion that is the main factor increasing the air resistance of vehicles, so it is not possible to obtain a significant effect of reduction in the air resistance, which is the object of the pneumatic tire disclosed in Japanese Unexamined Patent Application Publication No. 2010-260378A.